The invention relates to an apparatus for location and control of an appliance, as is preferably used for endoscopy or microsurgery.
Microsurgical and endoscopic instruments which are used in medicine are used in particular for diagnosis and during operations on sensitive tissues and organs to which access is difficult. These actions are generally computer-controlled and/or camera-controlled and normally require a very high degree of precise location, positioning and movement of the instruments. Probe systems such as magnetic or electromagnetic probes are used for this purpose. By way of example, U.S. Pat. Nos. 5,836,869 and 6,248,074 disclose fixed magnetic field sources and magnetic field sensors, respectively, which measure the three spatial coordinates of a moving magnetic field by means of a three-axis configuration of the magnet or, respectively, of the sensor. However, this does not allow spatially exact location of the endoscopic appliance at an accurate time. This is explained by the fact that the determination of the magnetic field co-ordinates as described in U.S. Pat. No. 5,836,869 necessitates the measurement of three different magnetic fields for a three-axis magnet which, in order to avoid superimposition, must be measured successively at different times, by the individual axes producing electromagnetic signals at different times. The measurement is in this case carried out outside the patient and also requires a conversion operation in order to make it possible to estimate the position of the endoscope in the body.
U.S. Pat. No. 6,248,074 discloses a magnetic field source being mounted outside the patient; the location process is in this case carried out by determination of the relative position of the detector with respect to the external magnetic field by means of a magnetic field sensor which is fitted to the distal end of the endoscope. In this case as well, only a relatively inaccurate measurement is possible, since the endoscope and sensor are moved with respect to the fixed magnetic field, so that there is no exact relationship between the fixed magnetic field co-ordinates and the variable spatial alignment of the sensor. Furthermore, there are additional impeding factors which adversely affect the accuracy, for example the problem of measuring regions at different distances from the body surface, or the adverse effect on measurement accuracy resulting from external magnetic fields. In contrast, probes which are introduced into the body interior are often very sensitive, but require complicated electrical cable systems or the continuous use and replacement of the batteries.